In etching patterns in a masked substrate, some etching processes, such as ion beam milling, may also etch the mask, even when not desired. This is further compounded by the fact that a photoresist mask layer may etch faster than the substrate. One way to assure that the photoresist layer survives long enough to protect the underlying substrate is to make the photoresist thicker. The problem which arises when patterning a narrow line to be etched in the substrate with thick photoresist is that the walls (the profile) of the photoresist are not vertical, as shown in FIG. 1(a). The width of the photoresist near the substrate is greater than the width of the photoresist at the top of the resist. As a result, upon ion beam milling, a portion of the photoresist will be etched away along with the substrate, as shown by dotted line in FIG. 1(b), resulting in the etching of a narrower line width in the substrate than desired as shown by the dotted line in FIG. 1(c).